1. Field of the Invention
The present invention relates to code divisional multiple access (CDMA) cordless telephone systems and methods of operating such systems and is useful in particular for mobile CDMA telephone systems in which transmit and receive signals are exchanged, as radio signals or through a signal conduit, between a basestation, connected to a public switched telephone network, and a CDMA mobile telephone cordless handset. The signal conduit may, for example, comprise a co-axial cable or an optical fibre cable in a cable television (CATV) plant, and the CDMA telephone system may, for example, be an IS-95 or a 1.9 Ghz PCS CDMA system.
2. Description of the Related Art
It is known to provide telephone communication between a mobile cordless telephone handset and a basestation interfacing to a public switched telephone network, and to transmit CDMA transmit signals as wide area wireless signals to the handset. The mobile handset, timing is slaved to that of the transmit signals, and sends radio signals to the basestation for conversion and connection to the public switched telephone network. Such a system is commonly known as a macrocell system.
It is also well known to exchange signals with the mobile handset as radio signals between the handset and one or more RF repeaters in the form of remote antenna drivers (RAD's) through a CATV plant and a remote antenna signal processor (RASP) connected to the basestation. The use of RAD's can be arranged to provide a wide area (i.e. macrocell) service or to permit a plurality of small area wireless coverage zones, commonly referred to as microcells.
Prior art RAD-RASP technology connects the basestation to the RASP, and the RAD to the mobile handset, via a series of heterodyne operations. Thus, the basestation transmit signal is heterodyned to a frequency acceptable to the CATV plant by the RASP, and the RAD heterodynes the CATV transmit frequency to the correct radio frequency, etc.
RAD-RASP systems which perform identical heterodyne operations and which interconnect to the same basestation perform a simulcast transmission and reception. Consequently, they operate to form a macrocell. Microcells may be formed by using a lesser number of RAD's in the simulcast.
In prior art RAD-RASP systems, the location of the mobile handset can be determined only to the level of the cell. Therefore, microcells provide a relatively good resolution of the geographic location of the mobile handset.
Determination of the mobile handset may often be desirable. For example, it permits a wireless telephony operator to offer different billing rates for "in-home" and "out of home" usage of the mobile handset. However, in prior art RAD-RASP systems, this requires a large bandwidth on the CATV plant, since the microcells are distinguished from one another by heterodyning to different CATV transport frequencies.
Prior art RAD-RASP systems are described in U.S. Pat. Nos. 5,390,235 and 5,377,255, the disclosures of which are herein incorporated by reference.